About a third of hospital trusts are failing to reach their targets for treating 90% of patients within 18 weeks of referral by their GP, it was reported.

Data for April shows 51 trusts breaching waiting time limits – compared with 26 trusts a year ago, according to the BBC.

Despite this rise, overall the NHS is still meeting its target because many hospitals are performing better than required. On average across England, 90.5% of patients are seen within the limit.

But in the worst performing area – Hastings and Rother in Sussex – more than a quarter of patients are waiting longer than 18 weeks. The most acute problems are occurring in London, the south-east, the south coast and north-west.

Although last year Andrew Lansley, the health secretary, scrapped the 18-week limit as an official target, which had been set by the Labour government, he said that hospitals should still stick to it as part of the NHS Constitution commitment to patients. Speaking to the BBC, John Appleby, of the King's Fund health thinktank, predicted the problem would probably get worse. "I would guess it will keep going up. In the end, the government will probably have to start getting tougher if it wants to keep to the 18 weeks. It surprises me more patients aren't challenging this now it is a right," he said.

Peter Carter, head of the Royal College of Nursing, has called for the worst-performing hospitals to be merged, reorganised or simply shut down altogether.

"In our metropolitan areas we have far too many acute hospitals. That's a drain on the system and it has got to change" said Carter, speaking to the centre-right thinktank Reform this week.

Although his comments were echoed by Chris Ham, the chief executive of the King's Fund health thinktank, the Department of Health said that the government did not plan any hospital closures, since changes to the NHS needed to be locally-led.